High voltage liquid dielectrics of petroleum origin: Their manufacture and evaluation

The purpose of electrical insulation is to prevent passage or leakage of electrons from conductors. Insulators are characterized by a scarcity of free electrons in their physical structure and they can be considered as conductors of very high resistivity. Compared with gases, pure non-ionic liquids have the advantage of much greater density so that leaking electrons are hindered from passing by the molecules of the liquid. Solid cellulosic-type insulation also hinders the movement of electrons, but contains voids which must be completely filled with liquid dielectric, otherwise when subjected to an electric stress, these voids will permit gas-phase ionization, which is destructive to cellulose. In modern high voltage compact power transformers and cables the liquid dielectric constitutes an integral part of the insulation.